An optical spectrometer is a system that is used to sample the spectral components of an optical signal. In a general case, dispersive spectrometers use a dispersive element such as a diffraction grating to spatially distribute the spectral components of the optical signal. These spectral components are then measured by a linear array of detector elements, also known as a detector array.
Spectrometers that are built using discrete free-space optical components such as gratings and lenses are typically designed to measure only the wavelength content of one optical signal in one way, for example with a characteristic dispersion over a fixed operating bandwidth. In one example, these conventional spectrometers are typically not designed to measure both the spectrum and the polarization state of light in the optical signal. Polarization describes the orientation of the oscillation of the light wave's electric field. The polarization of light can be described using a combination of two orthogonal basis states. While there are some spectrometers that split the light signal into two polarization states and measure the spectral components for each polarization, these spectrometers use more optical components and/or require additional signal processing. As a result, the polarization needs to be controlled and managed at each interaction between a free-space beam and an optical surface, and this is generally a costly and difficult task using free-space optics.